The present invention, which might better be termed a discovery, can be fully comprehended when viewed in the light of the historical development of the photocomposition art. This background discussion is not a comprehensive treatise on all such development, but that which will show the area neglected, into which the present invention falls.
The broad term "photocomposition" can be applied even to the quite ancient art of portrait and snapshot photography. One making an exposure of film in a camera, and wishing to make a print other than the exact size of the film negative from the camera, may place that film negative into a projection device, generally termed an enlarger, and then adjust the distance of the film holder from the sensitive paper holder, and "focus" the picture by moving the lens relative to the film and paper.
The photocomposition term is generally now applied to the setting of printing text for cold type. The term will be used in that sense hereinafter. In order to produce a line of text, the photocomposition machine establishes a font holder plane and a sensitive film or paper plane. These two are not alterable in distance, as in a photo enlarger. Hence, early phototypesetting machines produced print in one size only, which was established by the distance between the font and paper, and the particular lens situated to project the image.
Early in the development of the art, it became apparent that the point size of the projected image could best be changed by changing the lens, rather than supplying a different size font source. By 1950, an application was made which ultimately issued as U.S. Pat. No. 2,790,362 for a machine employing a turret arrangement whereby multiple lenses were made available for the purpose of providing multiple point size projection. There may have been earlier teachings, but this is one of those teaching changeable lenses.
About the same time in the development of phototypesetting, the placement of type across the page began to receive considerable attention. Either the photosensitive sheet had to be moved laterally in order to position the characters in the composition one after the other, or the projected beam was required to be diverted across the page. Both approaches had considerable following. Beam diverting has been done by physically transporting the font, and by beam deflection. Deflecting of the beam has been developed to a fine degree of perfection in order that the physical mass of the paper holder or the projection device could be avoided.
With the development of various means to place the characters across a column of composition, came the development of means to space proportionally between letters and words. Proportional spacing is done to justify a column for the purpose of producing a pleasing uniform margin on left- and right-hand sides of the column. Much development attention has been given to this portion of photocomposition.
Another means for placing the letters along a row of composition was taught by U.S. Pat. No. 2,670,665. This teaching was of a collimating lens placed such that its focal plane was at the plane of the image font. Thus, the lens projects a column beam which is unintelligible until intercepted by another lens known as a decollimating lens. Because such decollimating lenses are lighter in weight than the paper or font carriages, a lens carriage shiftable the length of a desired printing column is easily moved in an escapement path back and forth the width of the printing column. The decollimating lens is coupled with a diverting mirror or prism to project the image into a focal plane laterally of the carriage movement path.
This escapement concept produced good placement of the images and did it quite rapidly, but taught no point size change concept.
Therefore, one is left with the inescapable conclusion that if the collimating escapement concept is to be employed, the collimating lens must be manually changeable. A turret of changeable lenses might be employed to swing into position if somehow the turret of lenses could be arranged such that the focal length of each lens would fall on the same font image plane. This is not a problem with the ancillary teaching of the developments taking place, because the turret lens concept being taught were focusing lenses not collimating lenses.
The turret concepts have always suffered from alignment problems in that the turret is a mechanical device and exact placement of the lens by the turret cannot be precisely precalculated but must be manually adjusted to position correctly during manufacture.